U.S. patent application number 09/941931 was filed with the patent office on 2002-06-20 for reproduction equipment, reproduction equipment specifying equipment, reproduction equipment specifying system and methods and recording media for said equipment and system.
Invention is credited to Arimura, Koji, Inoue, Hisashi, Katsura, Takashi, Kodono, Shinya, Nakamura, Kazuhiko, Noridomi, Kenichi.
Application Number | 20020076082 09/941931 |
Document ID | / |
Family ID | 18752312 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020076082 |
Kind Code |
A1 |
Arimura, Koji ; et
al. |
June 20, 2002 |
Reproduction equipment, reproduction equipment specifying
equipment, reproduction equipment specifying system and methods and
recording media for said equipment and system
Abstract
A reproduction equipment converts an identification code of the
reproduction equipment into a plurality of signal sequences using a
correspondence table and embeds the obtained plurality of signal
sequences in AV signals as a digital watermark. A reproduction
equipment specifying equipment compares correlation values of the
AV signals, containing the digital watermark embedded therein with
all signal sequences contained in a correspondence table. A
comparison of the correlation values with a previously set
threshold value determines the embedded signal sequences and the
identification code of the reproduction equipment which may be
extracted.
Inventors: |
Arimura, Koji; (Fukuoka-ken,
JP) ; Inoue, Hisashi; (Fukuoka-shi, JP) ;
Noridomi, Kenichi; (Fukuoka-shi, JP) ; Katsura,
Takashi; (Fukuoka-Shi, JP) ; Kodono, Shinya;
(Nishinomiya-shi, JP) ; Nakamura, Kazuhiko;
(Hirakata-shi, JP) |
Correspondence
Address: |
MORRISON LAW FIRM
145 North Fifth Avenue
Mt. Vernon
NY
10550
US
|
Family ID: |
18752312 |
Appl. No.: |
09/941931 |
Filed: |
August 29, 2001 |
Current U.S.
Class: |
382/100 ;
348/E7.056; 386/E5.004 |
Current CPC
Class: |
H04N 7/1675 20130101;
H04N 2005/91335 20130101; H04N 21/4331 20130101; H04N 5/913
20130101 |
Class at
Publication: |
382/100 |
International
Class: |
G06K 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 1, 2000 |
JP |
2000-264979 |
Claims
What is claimed is:
1. A reproduction equipment comprising: a digital watermark
generating means; said digital watermark generating means including
means for generating a digital watermark containing attribute
information that specifies a reproduction equipment; a digital
watermark embedding means; said digital watermark embedding means
including means for generating watermark-embedded AV signals which
embeds said digital watermark in said AV signals; and output means
for outputting said watermark-embedded AV signals to an
exterior.
2. A reproduction equipment comprising: a coded signal input unit
for receiving coded AV signals; a decoding unit including means for
reproducing said AV signals from said coded signal input unit; an
identification code generating unit including means for generating
an identification code by which a reproduction equipment can be
specified; a digital watermark embedding unit including means for
embedding said identification code as a digital watermark in said
AV signals input from said decoding unit; and an output unit, which
outputs to an exterior, AV signals containing embedded therein said
digital watermark prepared by said digital watermark embedding
unit.
3. A reproduction equipment as set forth in claim 2, wherein said
identification code is at least one of an equipment ID of said
reproduction equipment, a card ID of an IC card connected to said
reproduction equipment, a user ID of a user, a raw material ID of
said AV signals, a medium ID of a recording medium in which said AV
signals are stored, a reproduction date and time, and an initial
value of a signal sequence to be embedded as said digital
watermark.
4. A reproduction equipment as set forth in claim 2, wherein an
output of said identification code generating unit includes a
plurality of signal sequences, and a table of correspondence of at
least one of character strings and numbers, that express
identification codes, and means for employing a correspondence for
selection of said signal sequences.
5. A reproduction equipment as set forth in claim 4, further
comprising: means for converting said identification code into a
binary bit string; and means for selecting a plurality of signal
sequences, which correspond to the positions of the converted bit
string that take on a specific value.
6. A reproduction equipment as set forth in claim 4, wherein said
plurality of signal sequences are signal sequences with which cross
correlation values are smaller than a previously set threshold
value.
7. A reproduction equipment as set forth in claim 4, wherein said
digital watermark embedding unit embeds a different signal sequence
in each of a predetermined unit of said AV signals.
8. A reproduction equipment as set forth in claim 7, wherein said
digital watermark embedding unit embeds a plurality of signal
sequences, to be embedded as the digital watermark, randomly at a
same proportion per fixed time in said AV signals.
9. A recording medium as set forth in claim 1, further comprising
means for recording a copy of said watermark-embedded AV signals
that are recorded by said reproduction equipment.
10. A reproduction equipment specifying equipment comprising: an
input unit; means for inputting AV signals containing an
identification code embedded therein as a digital watermark; a
signal sequences recording unit; said signal sequences recording
unit including means for holding a correspondence table of the same
contents as that of a reproduction equipment; a correlation value
calculation unit including means for calculating correlation values
of input AV signals and all of said signal sequences contained in
said correspondence table and for outputting a maximum correlation
value among correlation values obtained; a threshold value setting
unit including means for setting a threshold value for said
correlation values; a comparison unit including means for comparing
said maximum correlation value with said threshold, and for
outputting a one of said signal sequences for which said maximum
correlation value exceeds said threshold value; an identification
code judgment unit including means for determining an
identification code in accordance to said signal sequences output
from said comparison unit and said correspondence table; and an
identification code output unit including means for outputting said
identification code.
11. A reproduction equipment specifying system comprising: a
reproduction equipment; said reproduction equipment including a
reproduction equipment specifying equipment; said reproduction
equipment specifying equipment including attribute information that
enables specifying at least one attribute of said reproduction
equipment; means in both said reproduction equipment and said
reproduction equipment specifying equipment for containing said
attribute information; said reproduction equipment including means
for embedding in an AV signal, as a digital watermark, said
attribute information that enables specifying said reproduction
equipment to an exterior; and said reproduction equipment
specifying equipment including means for extracting said digital
watermark embedded in said AV signal and for specifying said
reproduction equipment associated with said AV signal based on the
extracted digital watermark.
12. A reproduction method, comprising: generating a digital
watermark; the step of generating a digital watermark including
generating a digital watermark containing attribute information
that enable specifying of a reproduction equipment; embedding said
digital watermark in AV signals to produce watermark-embedded AV
signals; and outputting said watermark-embedded AV signals to an
exterior.
13. A reproduction method, comprising; inputting coded AV signals;
decoding said coded AV signals to reproduce said coded AV signals;
generating an identification code; embedding a digital watermark
containing said identification code in said input AV signals; and
outputting said AV signals containing said digital watermark.
14. A reproduction method as set forth in claim 13, wherein said
identification code is at least one of an equipment ID of a
reproduction equipment, a card ID of an IC card connected to said
reproduction equipment, a user ID of a user, a raw material ID of
said AV signals, a medium ID of a recording medium in which said AV
signals are stored, a reproduction date and time, and an initial
value of a signal sequence to be embedded as said digital
watermark.
15. A reproduction method as set forth in claim 13, wherein: the
step of generating an identification code includes using a
plurality of signal sequences, and a table of correspondence of at
least one of character strings and numbers that express
identification codes to select a one of said plurality of said
signal sequences.
16. A reproduction method as set forth in claim 15, further
comprising: converting said identification code into a binary bit
string; and selecting a plurality of signal sequences, which
correspond to positions of said converted bit string that take on a
specific value.
17. A reproduction method as set forth in claim 15, wherein the
plurality of signal sequences are signal sequences having cross
correlation values that are smaller than a previously set threshold
value.
18. A reproduction method as set forth in claim 15, wherein the
step of embedding includes embedding a different signal sequence in
each of a predetermined unit of the AV signals.
19. A reproduction method as set forth in claim 18, wherein the
step of embedding includes embedding said plurality of signal
sequences randomly at the same proportions per fixed time in said
AV signals.
20. A recording medium, in which watermark-embedded AV signals are
recorded by the reproduction method of claim 12.
21. A reproduction equipment specifying method, comprising:
inputting AV signals containing an identification code embedded
therein as a digital watermark; holding a correspondence table of
the same contents as that in a reproduction equipment, calculating
correlation values of the input AV signals and all signal sequences
included in said correspondence table and outputting a maximum
correlation value among said correlation values; setting a
threshold value for said correlation values; comparing said maximum
correlation value with said threshold value and outputting a one of
said signal sequences for which said maximum correlation value
exceeds said threshold value; determining an identification code in
accordance with said one of said signal sequences with contents of
said correspondence table; and outputting said determined
identification code.
22. A method for operating a recording medium, in which a
reproduction program is recorded, comprising: generating a digital
watermark containing attribute information, by which a reproduction
equipment can be specified; embedding said digital watermark in AV
signals to produce watermark-embedded AV signals; and outputting
said watermark-embedded AV signals to an exterior.
23. A recording medium, in which a reproduction equipment
specifying program is recorded, comprising: inputting AV signals
containing an identification code embedded therein as a digital
watermark; holding a correspondence table of a same contents as
that in a reproduction equipment, calculating correlation values
between the input AV signals and all signal sequences included in
said correspondence table and outputting a maximum correlation
value among correlation values obtained; setting a threshold value
for said correlation values; comparing said maximum correlation
value with said the set threshold value and outputting a signal
sequence for which said maximum correlation value exceeds said
threshold value; determining an identification code in accordance
with said output signal sequence and said correspondence table; and
outputting said identification code.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention concerns reproduction equipment for AV. In
the present specification, the term "AV" signals refers to either
audio or video or both audio and video (the form in which these
coexist is arbitrary). To be more specific, the invention concerns
an art of embedding an identification code, etc., which specifies a
reproduction equipment, as a digital watermark in AV signals
(reproduced signals) output from the reproduction equipment.
[0003] This invention also concerns equipment which specifies the
reproduction equipment, which extracts a digital watermark from
reproduced AV signals, and which specifies the reproduction
equipment that produced the AV signals (reproduced signals).
[0004] In the present Specification, "reproduction equipment"
refers not just to equipment that have only the function of
reproducing AV signals from a recording medium but refers
inclusively to equipment having both the function of reproduction
and the function of recording AV signals in a recording medium.
[0005] 2. Description of the Related Art
[0006] Recently, it has become possible to record and reproduce AV
data in various forms. AV data can be recorded and reproduced as
analog signals, as in the case of VHS, or recorded and reproduced
as digital signals, as in the case of DVD.
[0007] Also, the AV data may consist of just audio signals or video
(moving pictures or still pictures) signals and can be recorded and
reproduced as analog signals or digital signals.
[0008] This invention can be applied to AV data of the various
abovementioned signal forms.
[0009] In particular, digital contents (AV data in the form of
digital signals) have come to be used widely recently.
[0010] Regardless of whether the data that are recorded and
reproduced as AV data take on an analog or digital form, if the
data have the property of being an authored work, the copyright
thereof must be protected. The prohibition of illegal copies is
especially important.
[0011] Although AV data that take the form of analog signals can be
copied, the degradation of quality (sound quality or picture
quality, etc.), with each generation, cannot be avoided when
copying is performed. It can thus be said that excessive copying of
analog AV data cannot be performed readily.
[0012] However, quality degradation from copying does not occur at
all with digital contents. In other words, a copy that is exactly
the same as the original is easy to make.
[0013] Since illegal copies of contents (or contents that originate
from such contents and are distributed) cannot be distinguished
from the original, it is difficult to provide evidence that proves
their illegality. The establishment of technical methods that
enable effective protection of copyrights is thus being
demanded.
[0014] The use of "digital watermarks" is being examined as such a
method.
[0015] A "digital watermark" consists of data that are embedded in
AV data in a manner that is imperceptible to a viewer or listener
and are devised so that the digital watermark can be extracted from
the AV data in which it is embedded.
[0016] Copyright information (for example, the name of the
copyright holder, date of copyright, etc.) are embedded in AV data
as a watermark for protection of the copyright.
[0017] By extracting the embedded digital watermark (copyright
information) from AV data that are suspected to have been copied
illegally, the copyright holder, etc. of the contents are clarified
and the illegality of a copy is exposed. In such a manner, digital
watermarks are intended to prevent illegal copies.
[0018] Specific techniques for embedding a watermark in AV data are
described in detail, for example in "The Fundamentals of Digital
Watermarks--A New Protection Technology for Multimedia" by Kashio
Matsui (Morikita Publishing, 1998), etc.
[0019] Japanese patent publication No. 2982768 also discloses the
prevention of illegal copying of contents by embedding a digital
watermark in AV signals.
[0020] In the art described by this literature, an illegal copy
prevention control signal is embedded in advance as a digital
watermark in the AV signals.
[0021] Extraction of the illegal copy prevention control signal
from the AV signals is then performed during the reproduction of
the AV signals. If the copy prevention signal has been extracted
turns out to be illegal, noise is added anew as a digital
watermark.
[0022] Thus each time an illegal copy of a recording medium,
prepared based on the above art is viewed or listened to, noise is
added to the AV signals. This degrades the quality (sound quality
of visual quality) of the AV signals each time the signal is
reproduced or copied. Eventually, such a large amount of noise is
added to the AV signals that viewing and listening is impossible.
As a result, illegal copying in multiple generations is
prevented.
OBJECTS AND SUMMARY OF THE INVENTION
[0023] With the prior art, the reproduction equipment that was used
for copying cannot be specified. This is because, with the prior
art, the digital watermark that is embedded in the AV signals is,
for example, the name of the author, random noise without meaning,
etc. The embedded information has no relationship to the
reproduction equipment. Even if the digital watermark discloses the
name of the author, this information is of no practical use unless
proof can be obtained of the fact that illegal copying was
performed.
[0024] If the reproduction equipment that was used for copying can
be specified, it can be claimed with a high degree of certainty
that the owner or user of the reproduction equipment was involved
in illegal copying. However, the prior art is incapable of
providing this information.
[0025] Illegal copying therefore cannot be restrained effectively
by the prior art.
[0026] A first object of this invention is to provide an art which
can specify the reproduction equipment used for copying.
[0027] Generally in extracting the embedded digital watermark in
accordance with the abovementioned literature, the values of
correlation between all noise strings used in embedding and the
signals in which the digital watermark is embedded are determined
and the noise string that exhibits the greatest correlation value
is extracted as the embedded noise string. However, if the embedded
noise string is selected arbitrarily, there may be a noise string
that exhibits a high correlation value by chance. In this case, the
embedded noise string cannot be extracted accurately.
[0028] A second object of this invention is to provide an art by
which the embedded digital watermark can be extracted with high
precision.
[0029] In some cases, people who illegally copy AV signals
intentionally disable the extraction of the information embedded as
a digital watermark. For example, the signal sequence is
interchanged or a part of the signals is removed. When such
processing is performed, the embedded digital watermark cannot be
extracted correctly by the prior art.
[0030] A third object of this invention is to provide an art by
which a digital watermark can be extracted without fail even when a
third party processes the AV signals.
[0031] In some cases, people who perform illegal copying analyze
the embedded information or embedding method and intentionally
embed a false digital watermark. With the prior art, the protection
of the copyright is insufficient when a third party is successful
in analyzing the embedded information.
[0032] A fourth object of this invention is to provide an art that
contains a countermeasure for cases where a third party is
successful in analyzing the digital watermark.
[0033] A first mode of this invention provides a reproduction
equipment comprised of a digital watermark generating means, which
generates, as a digital watermark, attribute information that
enables the identifying the reproduction equipment, a digital
watermark embedding means, which generates watermark-embedded AV
signals with which the digital watermark generated by the digital
watermark generating means is embedded in AV signals, and an output
means, which outputs the watermark-embedded AV signals to the
exterior.
[0034] With the above arrangement, a reproduction equipment that
was used for illegal copying can be identified specifically by
means of the digital watermark that is extracted from illegally
copied AV signals. That the owner, etc. of the identified
reproduction equipment has been involved in illegal copying can
thus be claimed. A system for copyright protection can thus be
established to prevent illegal copying.
[0035] With a second mode of this invention, a reproduction
equipment identification code is converted into a plurality of
signal sequences using a correspondence table in the reproduction
equipment. The plurality of signal sequences obtained are embedded
as a digital watermark in the AV signals during reproduction. With
a reproduction equipment specifying equipment, the values of
correlation between the AV signals in which the digital watermark
was embedded and all of the signal sequences contained in the
correspondence table are determined and compared with a previously
set threshold value to determine the embedded signal sequences. The
identification code of the reproduction equipment is extracted
using a plurality of signal sequences obtained from AV signals of
at least a fixed length of time T.
[0036] With this arrangement, the identification code of the
reproduction equipment used-in the copying process can be extracted
from the illegally copied AV signals to enable detection and
prevention of illegal copying.
[0037] With a third mode of this invention, the signal sequences
with which the cross correlation values are smaller than a
previously set value (threshold value of cross correlation) are
used as the signal sequences to be embedded.
[0038] With this arrangement, the precision of extraction of the
embedded signal sequences by the reproduction equipment specifying
equipment is improved and the precision of extraction of the
identification code is improved. Identification of the reproduction
equipment is thus enabled.
[0039] With a fourth mode of this invention, a plurality of signal
sequences are embedded randomly by the reproduction equipment so
that they will be embedded at the same proportion per fixed time
T.
[0040] With this arrangement, even where people that perform
illegal copying perform the process of extracting parts of the AV
signals at fixed intervals, the identification code can be
extracted without fail from the illegally copied AV signals to
enable identification of the reproduction equipment.
[0041] With a fifth mode of this invention, the identification code
is converted into a bit string. A signal sequences corresponding to
the "1"s or the "0"'s of the bit string are embedded by the
reproduction equipment. The order of the embedded signal sequences
does not require a meaning.
[0042] With this arrangement, even where people that perform
illegal copying change the temporal sequence of the AV signals, the
identification code can be extracted without fail from the
illegally copied AV signals to enable identifying of the
reproduction equipment.
[0043] With a sixth mode of this invention, the contents of the
correspondence table that are held in the reproduction equipment
and the reproduction equipment specifying equipment are changed to
be always the same by means of a correspondence table changing
signal.
[0044] With this arrangement, even in the case where the embedded
signal sequences are leaked to a third party, new signal sequences
can be embedded by changing the correspondence table to enable
identifying of the reproduction equipment.
[0045] The above, and other objects, features and advantages of the
present invention will become apparent from the following
description read in conjunction with the accompanying drawings, in
which like reference numerals designate the same elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIG. 1 is a block diagram of a reproduction equipment
specifying system of an embodiment of this invention.
[0047] FIG. 2 is a block diagram of the reproduction equipment of
the invention.
[0048] FIG. 3 is a block diagram of the reproduction equipment
specifying equipment of the invention.
[0049] FIG. 4 is a flowchart for the reproduction equipment of the
invention.
[0050] FIG. 5 is a flowchart for the identification code generating
unit of the invention.
[0051] FIG. 6 is an example diagram of a correspondence table of
the identification code bit positions and signal sequences of the
invention.
[0052] FIG. 7 is an explanatory diagram of the identification code
bit positions of the invention.
[0053] FIG. 8 is a flowchart for the digital watermark embedding
unit of the invention.
[0054] FIG. 9 is an explanatory diagram which shows an example of
embedding signal sequences in video signals by the invention.
[0055] FIG. 10 is a flowchart for the reproduction equipment
specifying equipment of the invention.
[0056] FIG. 11 is a flowchart for the identification code judgment
unit of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0057] Referring to FIG. 1 a reproduction equipment specifying
system of the embodiment of this invention includes a reproduction
equipment 3 having an AV reproduction means 31. AV reproduction
means 31 is of a type capable of reproducing AV data moving in a
direction N I from an original recording medium 1. The AV signals
from AV signal reproduction means 31 are applied to a digital
watermark embedding means 33. A digital watermark generating means
32 applies a digital watermark to digital watermark embedding means
33. The digital watermark indicates attribute information by which
the recording equipment 3 can be specified. The method of
generating the digital watermark may be any conventional method,
such as that described in the book introduced in the section on the
related arts. What is important is that reproduction equipment 3
can be specified by this attribute information.
[0058] The resulting watermark-embedded AV signals are applied to
an output means 34. Output means 34 applies the watermark-embedded
AV signals to a reproduction device 6 and to an AV signal recording
equipment 4. A copier 10 reproduces the data on original recording
medium 1 using the output of reproduction equipment 3. In addition,
AV signal recording equipment 4 duplicates the performance of
illegal copying onto a copy recording medium 2.
[0059] Copy recording medium 2 is then available as physical
evidence of the illegal copying performed by copier 10 (represented
by a stick figure of the person doing the copying).
[0060] A reproduction equipment specifying equipment 5 is used to
prove the fact that copy recording medium 2 was prepared by copying
using reproduction equipment 3. Reproduction equipment specifying
equipment 5 includes an AV signal reproduction means 51 which
receives the copied output of copy recording medium 2. The output
of AV signal reproduction means 51 is watermark-embedded AV signals
which are applied to a digital watermark extraction means 52.
Digital watermark extraction means 52 derives the embedded digital
watermark from the watermark-embedded AV signals, and applies the
resulting digital watermark to a suitable reproduction device such
as, for example, a printing means 53 for printing the digital
watermark on paper. Printing means 53 may be any convenient
human-understandable device such as, for example, a computer
monitor, TV display. In some applications, a combination of display
for immediate review, and a permanent printed record may be
desired.
[0061] It is assumed in the following that copier 10 does not have
a copyright for recording medium 1 and that copier 10 can be
identified as an owner or user of reproduction equipment 3.
[0062] The form of the signal in original recording medium 1 and
copy recording medium 2 is arbitrary and may be either analog or
digital. The form of recording medium of recording medium I and
copy recording medium 2 is also arbitrary and may be selected
freely from among disks, tapes, hard disks, etc.
[0063] In general, reproduction equipment 3 may be of a type that
is distributed in large numbers in the market while reproduction
equipment specifying equipment 5 is generally owned by an
organization that controls the copyright for recording medium 1 or
by the police or other authority that exercises control over
copyright violations.
[0064] Although, for purposes of illustration, reproduction
equipment 3 and reproduction equipment specifying equipment 5 are
shown at the same location, reproduction equipment 3 and
reproduction equipment specifying equipment 5 normally exist in
separate locations. Usually, these equipments also differ in their
time of use.
[0065] With the system of this invention, illegal copying by copier
10 can be proven by the process to be described below.
[0066] With the system shown in FIG. 1, when copier 10 performs
illegal copying, copier 10 sets original recording medium 1 in
reproduction equipment 3, connects reproduction equipment 3 to AV
signal recording equipment 4 with a cable, etc., and sets copy
recording medium 2 in AV signal recording equipment 4.
[0067] Copier 10 also connects reproduction equipment 3 or AV
signal recording equipment 4 to a reproduction device 6 to monitor
the AV signals.
[0068] If the AV signals contain both sound and images,
reproduction device 6 may be television equipment. If the AV
signals contain only sound, reproduction device 6 may be an
amplifier and speaker (or headphone), etc.
[0069] As was mentioned above, the AV signals may be either analog
or digital signals, and a reproduction device 6 that is compatible
with the form of AV signals used will be used.
[0070] If copier 10 considers monitoring to be unnecessary,
reproduction device 6 may be omitted.
[0071] Even if copier 10 monitors the AV signals using reproduction
device .6, since the digital watermark data are embedded in the AV
data in a manner that is imperceptible to the viewer or listener as
was mentioned above, copier 10 cannot normally notice that a
digital watermark is being embedded in the monitored AV
signals.
[0072] The present invention does not degrade the quality of AV
signals by the digital watermark as in the prior art described in
the abovementioned patent publication. Thus if copier 10 simply
monitors the AV data recorded in recording medium 1 without
performing illegal copying, the monitored AV signals will retain
good quality.
[0073] This invention thus excels over the art of the
abovementioned patent publication in the point that good quality is
maintained as long as only legitimate monitoring is performed.
[0074] It can be readily understood that, when it is clear that the
digital watermark extracted from copy recording medium 2 indicates
attribute information unique to reproduction equipment 3, the
suspicion that copier 10, whose connection as the owner, etc. of
reproduction equipment 3, is involved in the illegal preparation of
copy recording medium 2 becomes provable.
[0075] Thus with this invention, by embedding attribute information
unique to reproduction equipment 3 as a digital watermark in the
reproduced AV signals, the copyright of recording medium 1 can be
protected effectively.
[0076] From the standpoint of copier 10, since copier 10 cannot
perceive that a digital watermark is being embedded even if he/she
monitors the AV signals on means of reproduction device 6, the
evidence of illegal copying is inscribed in copy recording medium 2
without the knowledge of copier 10.
[0077] A copier 10 who comes to know of these circumstances will
thereafter be discouraged to perform illegal copying heedlessly due
to his/her understanding of the likelihood of exposure of
participation in the illegal deed.
[0078] This invention can thus restrain illegal copying.
[0079] A representative form of coded AV signals is now taken up as
an example of the AV signals recorded in recording medium 1 and a
preferable embodiment for this type of AV signals is now described
in detail.
[0080] Referring to FIG. 2, AV reproduction equipment 3 includes AV
reproduction means 31, as previously described. AV reproduction
means 31 includes a coded signal input unit 101 which feeds a coded
signal to a decoding unit 102.
[0081] An identification code generating unit 103 receives the
output of decoding unit 102. An identification code generating unit
103 applies its output to digital watermark embedding unit 104. The
output of digital watermark embedding unit 104 is applied to the
input of an output unit 105. Identification code generating unit
103 receives a correspondence table changing signal whose nature
and function is described in detail later in this
specification.
[0082] With the present example, the coded signal input unit 101
and decoding unit 102 correspond to being the AV signal
reproduction means 31 of FIG. 1. Also, the identification code
generating unit 103 corresponds to being the digital watermark
generating means 32, digital watermark embedding unit 104
corresponds to being the digital watermark embedding means 33, and
output unit 105 corresponds to being the output means 34.
[0083] Referring now to FIG. 3, AV signal reproduction means 51
contains an input unit 201 which feeds its output to a correlation
value calculation unit 203 in watermark extraction means 52. A
signal sequences recording unit 202 feeds its output to correlation
value calculation unit 203. Signal sequences recording unit 202
receives a correspondence table changing signal, to be described
later. The output of correlation value calculation unit 203 is fed
to an input of a comparison unit 205. The output of comparison unit
205 is applied to an input of an identification code judging unit
206. The output of identification code judging unit 206 is fed to
an identification code output unit 207 in printing means 53.
[0084] With the present example, input unit 201 corresponds to the
AV signal reproduction means 51 of FIG. 1, the signal sequences
recording unit 202, correlation value calculation unit 203,
threshold value setting unit 204, comparison unit 205, and
identification code judgment unit 206 correspond to the digital
watermark extraction means 52, and identification code output unit
207 corresponds to the printing means 53.
[0085] The correlation value calculation unit 203 determines
correlation values S(k) defined as follows:
S(k)=.SIGMA.(Xi.times.Ni(k)) (i=1, 2, . . . , I)
[0086] where:
[0087] X: the AV signal sequences that is input
[0088] N: all of the signal sequences in the correspondence table;
e.g. N(k) k=1, 2, . . . , m
[0089] m: the number of signal sequences in the correspondence
table
[0090] The reproduction method by which an identification code is
embedded as a digital watermark in the AV signals is now described
with reference to the flowchart of FIG. 4 which illustrates the
process performed by the reproduction equipment of FIG. 2 in
embedding the identification code as a digital watermark.
[0091] Coded signal input unit 101 acquires a coded AV signals by
readout from a recording medium (for example, a DVD, DV, HDD,
etc.), receiving of a broadcast, or downloading from a network (for
example, the Internet). Coded signal input unit 101 sends the coded
AV signals to decoding unit 102 (step 301). Decoding unit 102 then
decodes the coded AV signals in accordance to the rules of
compression, transmission protocol, etc. and generates base-band AV
signals (step 302).
[0092] The process of identification code generating unit 103 (step
303) is now described with reference to the flowchart of FIG. 5,
which illustrates the flow of the process performed by
identification code generating unit 103.
[0093] Identification code generating unit 103 prepares, as
attribute information unique to the reproduction equipment, an
identification code from or by combining the equipment ID of the
reproduction equipment, the card ID of an IC card connected to the
reproduction equipment, the user ID of a user, the raw material ID
of the AV signals, the medium ID of the recording medium in which
the AV signals are stored, and the reproduction date and time (step
401).
[0094] For example, the equipment ID of the reproduction equipment
is set to "152". In this example, the number "152" is used as the
identification code.
[0095] This identification code is then converted into a binary bit
string consisting of "0"s and "1"s (step 402). When the equipment
code "152" is converted into a bit string, it becomes
"10011000".
[0096] The signal sequences corresponding to the bit positions of
the bit-converted identification code at which the bit value is 1
are searched from a previously prepared correspondence table (step
403).
[0097] FIG. 6 shows a correspondence table of the identification
code bit positions and the signal sequences. FIG. 7 shows the
identification code bit positions.
[0098] With the bit-string-converted identification code,
"10011000", since the 4th bit, 5th bit, and 8th bit (reading from
right to left) from the LSB take on a value of "1", the three
signal sequences {N4, N5, N8} are found to correspond to the bit
positions with a value of "1" by use of the correspondence table.
Identification code generating unit 103 sends these signal
sequences to digital watermark embedding unit 104 (step 404).
[0099] Although the identification code was converted to binary
form in converting the identification code into a bit string, the
method of conversion to a bit string is not limited thereto. For
example, a code table for the ASCII code, etc. may be used
instead.
[0100] Also, although signal sequences were prepared from bit
positions of value "1" in the search for signal sequences from the
correspondence table, the signal sequences may be prepared from bit
positions of value "0" instead.
[0101] The process of digital watermark embedding unit 104 (step
304) is now described with reference to the flowchart of FIG. 8,
which shows the flow of the process digital watermark embedding
unit 104. Digital watermark embedding unit 104 embeds the plurality
of signal sequences input from identification code generating unit
103 at the same proportion per fixed time T. This is done since the
signal sequences can then be taken out conveniently at fixed
proportions when AV signals of a fixed time T are taken out.
[0102] That is, the number of times EMAX by which each signal
sequences is embedded in a fixed time T is set (step 701) and the
number of times of embedding of each signal sequences is cleared to
0 (step 702).
[0103] One signal sequences is then selected randomly from among
the signal sequences for which the number of times of embedding is
not EMAX and the number of times of embedding of that signal
sequences is incremented (step 703).
[0104] The selected signal sequence is then embedded as a digital
watermark by a previously used method into a predetermined unit of
the AV signals input from decoding unit 102 (step 704).
[0105] The processes from the selection of signal sequences of step
703 are then repeated until the number of times of embedding equals
EMAX for all signal sequences. Then the next process is entered
(step 705).
[0106] If the embedding process of step 703 to step 705 is to be
repeated further, the process is repeated from the clearing of the
number of times of embedding of step 702, otherwise the embedding
process is ended (step 706).
[0107] Output unit 105 then outputs the AV signals, in which the
identification code has been embedded as the digital watermark by
digital watermark embedding unit 104, to a monitor, speaker,
recording equipment, network, etc. (step 305).
[0108] Referring now to FIG. 9, an example is shown in which the
signal sequences have been embedded in video signals. With this
example, the embedded signal sequences are {N4, N5, N8}, the unit
of the video signals in which one signal sequences is embedded (the
abovementioned predetermined unit) is 1 field, the fixed time T in
which the proportions of the respective signal sequences are made
the same is set to 9 fields, and each signal sequences is embedded
3 times within the 9 fields.
[0109] Although one signal sequences is embedded within 1 field as
the predetermined unit in this example, the predetermined unit may
be set to 1 frame or the predetermined unit may be set to several
fields or several frames.
[0110] Referring now to the flowchart of FIG. 10, the reproduction
equipment specifying method, by which the identification code is
extracted from the AV signals, in which the identification code was
embedded as the digital watermark, and the reproduction equipment
is specified, is shown. FIG. 10 illustrates the process performed
by the reproduction equipment specifying equipment of FIG. 3.
[0111] Input unit 201 sends the input AV signals to correlation
value calculation unit 203 upon dividing the signals into the
predetermined units, in each of which is embedded one signal
sequences (step 901). Signal sequences recording unit 202 has
recorded therein a correspondence table of identification code bit
positions and signal sequences of the same contents as that used in
the reproduction equipment.
[0112] Correlation value calculation unit 203 determines the
correlation values of all signal sequences and the AV signals input
from input unit 201 and determines the maximum correlation value
from these correlation values (step 902). The maximum correlation
value and the bit position corresponding to the signal sequences
for which the maximum correlation value was extracted are then sent
to comparison unit 205.
[0113] For example, when the correspondence table of FIG. 5 is
used, correlation value calculation unit 203 determines the
correlation values of the m signal sequences {N1, N2, . . . Nm} and
the AV signals and determines the maximum correlation value from
among these correlation values. If the maximum correlation value
SMAX is obtained for the correlation with the signal sequence {N4},
this maximum correlation value SMAX and the bit position {4} that
corresponds to signal sequence {N4} are sent to comparison unit
205.
[0114] Threshold value setting unit 204 then sets a threshold value
for the correlation value of comparison unit 205 (step 903).
Comparison unit 205 compares the maximum correlation value with the
threshold value (step 904) and, if the correlation value exceeds
the threshold value, sends the bit position corresponding to the
signal sequences for which this correlation value was extracted to
identification code judgment unit 206. If the maximum correlation
value is less than or equal to the threshold value, the bit
positions are not sent.
[0115] When a disturbance occurs due to illegal copying, etc., a
correlation value greater than the threshold value may not exist at
all or a plurality of correlation values greater than the threshold
value may exist. In such a case, comparison unit 205 may be
programmed to not compare the threshold value and the correlation
value but perform, as an exceptional process, the extraction of the
bit position of a signal sequence with a maximum correlation value
S1 only in the case where the maximum correlation value S1
satisfies a certain condition with respect to the other correlation
values Sn (for example, the condition S1>Sn).
[0116] The process of identification code judgment unit 206 (step
905) is now described in detail with reference to the flowchart of
FIG. 11 which shows the flow of the process of identification code
judgment unit 206.
[0117] Identification code judgment unit 206 holds a plurality of
bit positions that were obtained by determining the correlation
with a plurality of signal sequences obtained from AV signals of a
fixed time T or more using at least the reproduction equipment
(step 1001). An identification code bit string is then generated
from the plurality of bit positions (step 1002). An identification
code is generated from the bit string (step 1003).
[0118] The interpretation and method of bit string preparation and
identification code generation are the same as those for the
reproduction equipment. For example, if the plurality of bit
positions obtained from an AV signal of a fixed time T is {4, 5,
8}, since signal sequences are embedded at bit positions
corresponding to the "1"'s in the identification code bit string by
the reproduction equipment, the bit string, "10011000", will be
obtained.
[0119] Also, since decimal to binary conversion is used in the
generation of the bit string at the reproduction equipment, the
identification code, "152", will be obtained from the bit string,
"10011000".
[0120] Identification code output part 207 then outputs the
identification code extracted by identification code judgment unit
206 (step 906).
[0121] Also in accordance with a correspondence table changing
signal, the identification code generating unit 103 of the
reproduction equipment and the signal sequence recording unit 202
of the reproduction equipment specifying equipment can change the
contents of the correspondence tables held. Such a change of the
correspondence tables can be accomplished by any method. Several
correspondence tables may be held in advance in each of
identification code generating unit 103 and signal sequence
recording unit 202. These correspondence tables may be
interchanged, or a new correspondence table may be input from the
exterior.
[0122] The changes of the correspondence tables in identification
code generating unit 103 and signal sequence recording unit 202 are
made simultaneously so as to make agreement between their
contents.
[0123] Thus even for the same identification code, different signal
sequences can be embedded as the digital watermark in the AV
signals at the reproduction equipment. The reproduction equipment
specifying equipment can thus be made to extract the embedded
identification code correctly.
[0124] Also, as the plurality of signal sequences used in the
correspondence tables in the identification code generating unit
103 of the reproduction equipment and the signal sequence recording
unit 202 of the reproduction equipment specifying equipment, signal
sequence are used with which the cross correlation will be smaller
than a previously set value (threshold value of cross correlation).
By selecting a signal sequence in which the cross correlation is
smaller, the precision of extraction of the embedded signal
sequences can be improved and the precision of extraction of the
identification code can be improved. Preferably, a PN code,
M-sequence code, or Gold code is used.
[0125] As has been described above, with the reproduction equipment
of the present embodiment, the decoding of coded AV signals is
performed, an identification code is converted into a plurality of
signal sequences using a correspondence table, and the plurality of
signal sequences thus obtained are embedded as a digital watermark
at the same proportion per fixed time T.
[0126] Meanwhile, with the reproduction equipment specifying
equipment, the correlation values of the AV signals in which the
digital watermark was embedded and signal sequences contained in
the correspondence table are determined and compared with a
previously set threshold value to determine the validity of the
embedded signal sequences.
[0127] The identification code of the reproduction equipment is
then extracted from the plurality of signal sequences obtained from
AV signals of a fixed time T or more.
[0128] Furthermore, the correspondence tables in the reproduction
equipment and the reproduction equipment specifying equipment are
changed simultaneously to the same contents. The signal sequences
to be embedded can thus be changed even for the same identification
code.
[0129] Having described preferred embodiments of the invention with
reference to the accompanying drawings, it is to be understood that
the invention is not limited to those precise embodiments, and that
various changes and modifications may be effected therein by one
skilled in the art without departing from the scope or spirit of
the invention as defined in the appended claims.
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